Electroplating and electrodeposition have been used to provide surface layers on parts of many types, including tubing used in manufacturing coaxial cables to shield the conductor in the cable from ambient signals that would adversely affect the performance of the cable. In a known tubular coating process a continuous tube is pulled through a bath solution with conductive metal ions therein, such as, for example, silver, gold, copper, nickel and others. A cathode (negative pole) connection of a DC power supply is made with the endless tube. An anode of the metal used in the coating process is connected to the anode (positive pole) of the DC power supply. A metal coating is applied during the process.
In the coating process, a normally metallic coating is applied to the surface of an object by the action of electric current. The deposition of a metallic coating onto an object is achieved by creating a negative charge on the object to be coated and immersing it in a solution containing a salt of the metal to be deposited. The object to be coated is made the cathode of an electrolytic cell. Since the metallic ions of the salt carry a positive charge, the ions are attracted to the object. When the ions reach the negatively charged object that is to be coated, the object provides electrons to reduce the positively charged ions to metallic form. The result is a metal coated surface on the charged object. Such processes are used frequently for individual discrete parts. However, it is also known to use such processes for coating continuous lengths of tubing such as the aforementioned tubing used for manufacturing coaxial cable.
Creating a continuous electrical contact with a moving endless tube has presented difficulties. Known conductive methods to apply a charge to a continuous moving tube have included the use of copper or phosphorus brushes. A continuous conductive link is required between the brush and the moving tube for proper tubular coating as the electrical charge passes through the brush to the moving tube. A problem known in the tube coating industry is that known methods of brush to tube conductive contact tend to be somewhat intermittent. Intermittent electrical contact with the moving tube can cause inconsistent metal coating on the surface and possibly even extended areas of poor coating or voids that have no coating. Known brush contacts for electroplating continuous tubing wear relatively quickly and require frequent replacement. Further, copper brushes that have been used conduct charge to the tube differently as the brush wears, requiring constant monitoring of the charge or voltage, and adjustment as necessary.
There is a need for an efficient, reliable conductive contact system that can be used effectively in an electrocoating process for moving endless tubing, which contact system is of long life and requires minimal service or replacement.